I think you are going “down the rabbit hole” with your reasoning.
Google isn’t interested in detecting spun content, they are interested in filtering duplicate content.
Nearly all content is spun content. It is either spun by the human brain or spun by software. There is nothing wrong with spun content as long as the content is of high quality, and that it is useful, relevant and used in a responsible fashion.
For the sake of diversity and purpose of conserving resources, Google will filter identical, or nearly identical results from SERPs and limit the amount of duplicate content that will be indexed. This is not a direction they have been heading in, they have been doing this since their inception. It’s only your perception of this possibility that is new.